In order to decrease the emission of nitrogen oxides, modern motor vehicles often have an exhaust gas system with exhaust gas recirculation. In such exhaust gas systems a proportional quantify of the exhaust gas generated by an internal combustion engine of the motor vehicle is recirculated to the intake air of the internal combustion engine. The mixture of intake air and exhaust gas has a lower oxygen content than the pure intake air as a result of which the combustion temperature in the internal combustion engine is lowered. The result of the lower combustion temperature is a decrease in the oxidation of nitrogen during the combustion process, thus lowering the production of environmentally harmful nitrogen oxides.
In gasoline engines, exhaust gas recirculation can also result in a redaction in the specific fuel consumption in partial load mode. The lower oxygen content of the mixture in the internal combustion engine allows the throttle valve to stay open longer in partial load mode, so that back pressure losses that reduce the efficiency of the internal combustion engine are eliminated at the throttle valve.
An especially good effect of exhaust gas recirculation is obtained, when the recirculated exhaust gas is cooled by means of an exhaust gas recirculation cooler, because as the exhaust gas cools down, its density increases. Since the combustion of hydrocarbons produces, besides CO2, significant quantities of water vapor, the situation may arise that the vapor condenses as the exhaust gas cools down, so that liquid water collects in the exhaust gas system.
If, additionally, the charge air is compressed before entering into the internal combustion engine, then the condensed water can flow into the compressor from the exhaust gas recirculation line. Owing to the high rotational speeds of modern compressors, the result may be corrosion or total destruction of the compressor.
In order to avoid the aforesaid, the condensed water has to be removed from the exhaust gas recirculation line. EF 1 548 269 A1 discloses an exhaust gas system wherein a condensate trap is used to separate the water from an exhaust gas recirculation cooler of the exhaust gas system. Such condensate traps are complicated in design as well as difficult and expensive to manufacture.
As an alternative to the use of condensate traps, the exhaust gas recirculation line can also have a collecting tank in which the condensed water collects. A drain line can deliver the water from the collecting tank to the environment or can recirculate it into the exhaust gas line. An exhaust gas system with such a collecting tank is known from U.S. Pat. No. 4,055,158. In such an exhaust gas system, not only the collected water but also a sizable portion of the exhaust gas to be recirculated flows through the drain line, so that the effect of the exhaust gas recirculation is reduced.
Thus, the object of the present invention is to provide a motor vehicle that makes it possible to remove the condensed water from the recirculated exhaust gas in an especially simple and efficient way.